Spectral and photochemical properties of borohydride-treated D1-D2-cytochrome b-559 complex of photosystem II.
The D1-D2-cytochrome b-559 reaction center complex of photosystem II with an altered pigment composition was prepared from the original complex by treatment with sodium borohydride (BH4-). The absorption spectra of the modified and original complexes were compared to each other and to the spectra of purified chlorophyll a and pheophytin a (Pheo a) treated with BH4- in methanolic solution. The results of these comparisons are consistent with the presence in the modified complex of an irreversibly reduced Pheo a molecule, most likely 13(1)-deoxo-13(1)-hydroxy-Pheo a, replacing one of the two native Pheo a molecules present in the original complex. Similar to the original preparation, the modified complex was capable of a steady-state photoaccumulation of Pheo- and P680+. It is concluded that the pheophytin a molecule which undergoes borohydride reduction is not involved in the primary charge separation and seems to represent a previously postulated photochemically inactive Pheo a molecule. The Qy and Qx transitions of this molecule were determined to be located at 5 degrees C at 679.5-680 nm and 542 nm, respectively.
Shkuropatov
A Y
AY
Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region, Russian Federation. shkur@issp.serpukhov.su
Khatypov
R A
RA
Volshchukova
T S
TS
Shkuropatova
V A
VA
Owens
T G
TG
Shuvalov
V A
VA
D001894:Borohydrides / Q000378:metabolism; D019663:Chenopodiaceae / Q000378:metabolism*; D002734:Chlorophyll / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D003573:Cytochrome b Group / Q000378:metabolism*; D004227:Dithionite / Q000494:pharmacology; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010269:Paraquat / Q000378:metabolism; D010674:Pheophytins / Q000737:chemistry / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry
D001894:Borohydrides; D003573:Cytochrome b Group; D045342:Light-Harvesting Protein Complexes; D010674:Pheophytins; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D004227:Dithionite; C061694:pheophytin a; C025364:sodium borohydride; C019313:cytochrome b559; D010269:Paraquat; D000077194:Chlorophyll A